1. Field of the Invention
This invention relates to appliances and, more particularly, to a vent assembly for controllably discharging combustion gases generated through operation of these appliances.
2. Background Art
Many different vent assemblies currently exist for controllably discharging combustion gases generated by fuel burning appliances. Several variations of these vent assemblies are used, for example, on water heaters.
In one known construction, a hood at the inlet to a vent conduit is situated directly above a flue outlet in de-coupled relationship. That is, there is a gap between the flue outlet and the vent pipe inlet. This design has the advantage that backflow/downdraft pressure is dissipated by reason of the backflow being able to disburse around the hood at the vent pipe inlet without creating a detrimental capping pressure at the flue outlet. In the absence of controlling this capping pressure, combustion within the appliance may be adversely affected. In a worst case, flame-out could occur.
One disadvantage with the above hood construction is that the draft height is less than it would be with the vent pipe inlet directly connected to the flue outlet so that there is a continuous passage created between the combustion location and the vent pipe discharge location.
Depending upon the balance between the exhausting gas and backflow pressures, there is also a possibility that a significant volume of combustion gases may detrimentally leak into the space within which the appliance is operated.
As an alternative to the above hood construction, it is known to directly connect the flue outlet to the vent pipe inlet and to incorporate a flow/draft control assembly. The flow control assembly typically is a conduit portion that is. “T'ed” into the vent pipe to produce a diversionary path transverse to the main flow path of combustion gases from the appliance to the discharge location. The conduit portion generally has a configuration the same as the vent pipe from which it originates. The conduit portion will typically have a closure plate that pivots between opened and closed positions and is normally urged into the closed position.
As the appliance is operated and draft generated in the vent pipe, a low pressure region is created in the conduit portion that tends to urge the closure plate towards its open position and draw intake/dilution air from the space within which the appliance is operated. This intake/dilution air mixes with the discharging combustion gases and assists draft development to contribute to efficient venting of the appliance.
The conduit portion is also designed to relieve backflow pressure by allowing a limited passage thereof into the space in which the appliance is operated. The backflow impinges upon the closure plate to urge it towards the open position.
While the conduit portion does relieve to some extent the capping pressure at the flue outlet, the capping pressure is generally substantially higher than that encountered using the aforementioned hood construction. Thus, this system is prone to being adversely affected by backdraft conditions and flame-out.
The industry continues to seek out systems that will generate draft that contributes to efficient venting of the appliance, without experiencing adverse effects from backflow. Ideally, these goals are achieved without any significant diffusion of combustion gases into a space within which the appliance is located and operated.